1. Field of the Invention
The present invention relates to automatic audio visual equipment utilizing a visual image projector operating in synchronism with control signals and audio program signals recorded on a magnetic tape. More specifically, the invention relates to a microprocessor controlled system for regaining synchronization between the visual image projected and the audio program recorded on the magnetic tape.
2. Description of the prior art
A species of audi-visual equipment intended for educational use utilizes a compact cassette magnetic tape playback machine operating in synchronism with a visual image projector such as a slide or filmstrip projector. Typically, two types of signals are recorded on the magnetic tape. Audio signals are recorded to provide an audio instruction program to accompany the visual presentation, and cue tone bursts are recorded to provide signals to advance a slide or filmstrip frame at an appropriate point in the audio instruction program. Cue tone signals may also be provided for other instructional purposes.
The recording of the audio instruction program and the cue tones may be done in accordance with either a superimposed system or a separate track system as specified in American National Standards Institute (ANSI) specification PH 7.4-1975.
The super-imposed system provides for the recording of low frequency cue tone bursts on the same track as the audio instruction program. The cue tone burst may be recorded simultaneously with, and/or in sequential relation to the audio information signal. In the case of simultaneous super-imposed recording, the cue tone burst is recorded directly over the audio information signal. In the case of sequential super-imposed recording, the audio information signal is recorded between adjacent cue tone bursts. As used herein, the terms super-imposed, and mixed denote either simultaneous or sequential super-imposed recording. The cue tones consist of 50 Hz.+-.5% tone burst. The burst time duration is 0.45.+-.0.07 seconds for visual advance and 2.00.+-.0.25 seconds for visual advance and program stop. During playback the magnetic tape transport means transports the magnetic tape past the sensing surface of a playback head. The playback head picks up both the audio instruction program signals and the cue tones for reproduction. In order to prevent the lower frequency portion of the audio instruction program signals from being misinterpreted as a cue tone signal and causing spurious visual advance, the output of the playback head is passed thru one or more frequency responsive filters to effectively separate the audio signals from the control signals. The filter(s) may be a band pass filter having a center frequency of 50 Hz. The audio program may be passed through a high pass filter having a transition frequency of 125 Hz and a minimum attenuation rate of 24 db/octave then presented to the student thru a loudspeaker or earphone and the cue tone signals are used to provide visual advance synchronized with the audio program.
The separate track system records the audio program on a first track and the cue tone on a second track. A 1,000 Hz cue tone is provided for visual advance and a 150 Hz cue tone is provided to stop the program. In addition, a 400 Hz and a 2300 Hz cue tone may be provided for unassigned control purposes. A first reproduce head picks up the audio signals from the first track and a second reproduce head picks up the control signals from the second track. Frequency selective filters then separate the various cue tones to perform their intended control functions.
The superimposed and separate track systems both have advantages and disadvantages. The superimposed system allows for the maximum recorded audio instruction program time for each compact cassette but the frequency restricted cue tone limits the number of control functions. Also, it is very difficult to rearrange the cue tones once the superimposed audio program and cue tones have been recorded. The separate track system allows a larger number of control functions and permits convenient erasing and rearranging of the cue tones. However, the use of a separate track system reduces the amount of audio program material that can be recorded.
A draw back of existing audio visual equipment using the superimposed system is that it is difficult to maintain audio visual synchronization when returning to a prior art in the audio visual program, or when advancing to a subsequent point in the program.
The following two examples illustrate these drawbacks.
1. A student desires to return to a prior point in the audio-visual program to review material. Using the manual control provided on the projector the student decrements the visual presentation in the reverse direction until the desired visual presentation is reached. The tape transport is then rewound on a trial and error basis until the appropriate point on the audio program is located. The synchronized audio-visual program is then resummed.
2. A student desired to advance to a subsequent point in the audio visual presentation to avoid material previously learned. Using the manual control provided on the projector, the student increments the visual presentation in the forward direction until the desired visual presentation is reached. The tape transport is then fast forwarded on a trial and error basis until the appropriate point in the audio program is located. The synchronized audio-visual program is then resummed.
As is readily apparent, any departure from the predetermined audio-visual program requires the student to fast forward or rewind on a trail and error basis to locate the appropriate point in the audio program. It would be very desirable to provide means for automatically retaining or regaining audio-visual synchronization during or after rapid manual incrementing of the visual program in a forward direction or decrementing of the visual program in a reverse direction.
Conventional tape transports for compact cassettes, when in fast forward or fast rewind modes, provide a relatively constant angular velocity to the take up reel spindle. As the tape winds onto the take up reel, the effective radius of the take up reel increases. The linear velocity or speed of the tape being transported past the playback head is a function of the effective radius of the take up reel. During an end to end rewind or fast forward of a conventional compact cassette the linear tape velocity past the reproduce head can vary from approximately six to twenty-four times the normal tape playing speed of 1.875 in/sec (4.76 cm/sec). Thus the linear tape velocity can vary from a low of 11.25 in/sec (28.56 cm/sec) to a high of 45 in/sec (114.25 cm/sec). The frequency of the voltage induced into the playback head is directly proportional to the linear tape velocity past the head. During end to end rewind or fast forward of a conventional compact cassette the recorded 50 Hz cue tones can induce a signal ranging in frequency from 300 Hz to 1,200 Hz, and the low frequency portion of the audio program (125 Hz) can induce a playback signal ranging from 750 Hz to 3,000 Hz. Induced voltage frequency ranges of the cue tones and the audio program overlap. The 50 Hz filters used to separate the superimposed cue tones and audio program during normal playback can not be used during rewind or fast forward. A pre-set filter for the range of cue tone frequencies cannot be used since the overlapping audio program material can pass through the filter and be misinterpreted as a cue tone to cause a spurious visual advance count.
In U.S. Pat. No. 4,121,263 filed on July 27, 1977 and entitled Method and Apparatus for Control Signal Separation To Regain Synchronization Between A Visual Image Projector And An Audio Program, the contents of which are incorporated herein by reference, apparatus is described that enables the cue tones to be successfully separated from the audio program while the tape transport is operated in either the fast forward or fast reverse mode of operation. The apparatus described functions with a magnetic tape, as does the present invention, that contains either a superimposed system or a separate track system as described above. In U.S. Pat. No. 4,115,824 filed on July 7, 1977 and entitled Method For Regaining Synchronization Between A Visual Image Projector And An Associated Audio Playback Machine, the contents of which are incorporated herein by reference, a method of utilizing the cue tones separated from the tape at high tape speeds to regain synchronization between the projected image and the audio program while the tape travels at high speed is disclosed. In the method and apparatus described in these copending applications, it is necessary for the machine operator to change the projected image to the image prior to the desired image when the tape is to be moved in a reverse direction to regain synchronization. This requirement is confusing to the operator and can result in operator errors. Further, no provision is made to automatically return the projected image and sound program to a saved or Book-Mark location. Such a capability is useful in audio visual educational systems to automatically return to the beginning to the audio-visual program after it is completed, return to a selected portion of the audio-visual program for review or to select which one or two or more audio-visual programs recorded on a single filmstrip and magnetic tape is to be initiated.
Accordingly, one object of this invention is to provide improved apparatus for regaining synchronization between a projected image and an associated sound program recorded on a magnetic tape.
Another object of this invention is to provide improved apparatus for regaining synchronization between a projected image and an associated sound program recorded on a magnetic tape wherein the tape is automatically synchronized with the projected image whether the tape must be moved in either the forward or reverse direction.
Still another object of this invention is to provide improved apparatus for regaining synchronization between a projected image and an associated sound program recorded on a magnetic tape wherein said projected image is automatically returned to an operator selected reference image and the sound program of the reference image is automatically synchronized therewith under the control of an operator.
A further object of this invention is to provide improved apparatus for regaining synchronization between a projected image and an associated sound program recorded on a magnetic tape that utilizes a microprocessor to monitor and control image projection and magnetic tape transport apparatus.